1. Field
The following description relates to a pixel and an organic light emitting display device using the pixel.
2. Description of Related Art
Recently, various flat panel display devices having reduced weight and volume, as compared to cathode ray tubes, have been developed. Among these flat panel display devices, are liquid crystal display devices, field emission display devices, plasma display panels, and organic light emitting display devices, among others.
Among these flat panel display devices, the organic light emitting display device displays an image using organic light emitting diodes that generate light by the recombination of electrons and holes. Such an organic light emitting display device is driven at low power consumption and has rapid response times.
FIG. 1 is a circuit view showing a pixel of a conventional organic light emitting display device. In FIG. 1, transistors included in the pixel are NMOS transistors.
Referring to FIG. 1, the pixel 4 of the conventional organic light emitting display device includes an organic light emitting diode OLED, and a pixel circuit 2 that is coupled to a data line Dm and a scan line Sn to control the organic light emitting diode OLED.
The anode electrode of the organic light emitting diode OLED is coupled to the pixel circuit 2, and the cathode electrode thereof is coupled to a second power supply ELVSS. Such an organic light emitting diode OLED generates light having a predetermined brightness corresponding to current supplied from the pixel circuit 2.
The pixel circuit 2 controls an amount of current supplied to the organic light emitting diode OLED corresponding to the data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn. The pixel circuit 2 includes a second transistor M2 coupled between a first power supply ELVDD and the organic light emitting diode OLED, a first transistor M1 coupled between the second transistor M2 and the data line Dm and having a gate electrode coupled to the scan line Sn, and a storage capacitor coupled between the gate electrode and the first electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn, and the first electrode thereof is coupled to the data line Dm. The second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst. Here, the first electrode is either a source electrode or a drain electrode, and the second electrode is the other of the source electrode or the drain electrode. For example, if the first electrode is a drain electrode, the second electrode is a source electrode. When the scan signal is supplied from the scan line Sn, the first transistor M1 coupled the data line Dm is turned on to supply the data signal from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and the first electrode thereof is coupled to the first power supply ELVDD. The second electrode of the second transistor M2 is coupled to the other terminal of the storage capacitor Cst and the anode electrode of the organic light emitting diode OLED. The second transistor M2 controls the amount of current flowing from the first power supply ELVDD to the second power supply ELVSS via the organic light emitting diode OLED corresponding to the voltage stored in the storage capacitor Cst.
One terminal of the storage capacitor Cst is coupled to the gate electrode of the second transistor M2, and the other terminal thereof is coupled to the anode electrode of the organic light emitting diode OLED. The storage capacitor Cst is charged with a voltage corresponding to the data signal.
The conventional pixel as described above displays an image having a predetermined brightness by supplying current corresponding to the voltage charged in the storage capacitor Cst to the organic light emitting diode OLED. However, the conventional organic light emitting display device cannot display an image having a uniform brightness due to deviations of the threshold voltages of the second transistors M2 in different pixels of the display device.
When the respective pixels 4 have different threshold voltages, the respective pixels 4 generate light having different brightness despite receiving a same data signal, such that an image having a uniform or desired brightness is difficult to display.